This invention relates to the disposal of waste pickle liquor and, more particularly, to the production of stable liquid fertilizers from waste pickle liquors which remain after ferrous articles have been pickled, e.g., in dilute sulfuric acid pickling baths.
In the manufacture of ferrous metal articles in the form of sheet, strip, wire, rod, bar, section or tubing, for example, it is common practice to treat the surface thereof in an acid pickling bath such as aqueous solutions of sulfuric acid to remove scale or oxide from the surface of such shapes. That is, during manufacturing operations in which the ferrous metal articles may be heated and drawn or rolled, the surfaces of the ferrous metal articles become oxidized either by the hot rolling or drawing operations themselves or in heat treatments between operations. Such oxidation forms a scale on the surfaces of the articles. The oxide scale needs to be removed before subsequent drawing or rolling operations otherwise it becomes forced into the metal with resultant defects. Pickling is also necessary to remove oxide scale to reduce wear on tools. Pickling of ferrous metal articles is accomplished by immersing the metal in a bath or vat of dilute acid typically sulfuric acid usually on the order of 8 to 10% by weight sulfuric acid at a temperature in the range of 140.degree. to 160.degree. F. As the pickling bath continues to be used, the acid solution becomes charged with iron salts such as ferrous sulfate and gradually decreases in acid strength. When the strength of the bath decreases to about 5% or less sulfuric acid by weight, the bath is considered waste and must be pumped out and be replaced with a fresh acid solution.
Generally speaking, it has not proved economic to recover either the acid or the iron content of waste pickle liquor on any large scale. Consequently, the great bulk of the millions of gallons of waste pickle liquor produced every year in the manufacture of ferrous metal articles must be disposed of as waste. These materials are, of course, environmentally unacceptable, and thus they require special handling and their disposal costs are extremely high.